Positive shyness is a universal emotion with the specific social function of regulating our interactions by improving trust and liking, and showing politeness. The present study examined early infant production of coy smiles during social interactions as a measure of positive shy behavior. Eighty 4-month-olds were experimentally observed during three types of interactions in front of a mirror in which (1) the infant only sees him or herself, (2) the infant only sees the other person (mother, father, or stranger), and (3) the infant sees both him or herself and the other person. Infants produced more coy smiles during the interaction with a stranger than during the interactions with their mother or their father, or when they could see only themselves in front of a mirror. Infants also produced more coy smiles when they could see their self-reflection during the interaction than when they could not. Our results support the assumption that coy smiles indicate an early emerging emotional reaction with an important adaptive function during social situations involving novel persons and when special attention is given to the child.